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Cretaceous Hills is an area of low, gravel hills. Acidic seeps, which support some of the most interesting natural communities in the state, are found in this area. Seeps are caused when groundwater, percolating through this gravel, flows to the surface where it meets underlying sandstone. An abundant and diverse flora grows in these moist areas, including many unusual and rare species of orchids, mosses, and ferns, some with four foot-long fronds.

LOCATION:Southeastern tip of Illinois along the Ohio RIver; Massac and Pope counties.

The Cretaceous Hills RRA encompasses the southeastern tip of the state. The area is characterized by rolling hills of sand, gravel, and clay and bottomlands along the Ohio River.

In the Ohio River floodplain are areas of cypress swamp, floodplain forest, and flatwoods. Flatwoods are forests growing on hardpan clay, a soil that is wet in spring and dry and hard in summer. The trees are relatively small, reflecting the harsh soil conditions, and they tend to blow over because of their shallow root systems. The nature preserve in Fort Massac State Park has a large flatwood forest comprised of pin oak, swamp white oak, and post oak.

LANDCOVER : Predominant landcover types are cropland (32%), upland woods (31%), and grassland (24%). This site ranks fourth in percentage of upland woods, ninth for grassland, and fifth for bottomland woods. It has one of the lowest acreages for nonforested wetlands.

NATURAL AREAS : There are 19 Natural Areas. Important natural features include barrens, springs, lakes, ponds, and flatwoods.

BIOLOGICALLY SIGNIFICANT STREAMS : Two stretches of the Ohio River totalling 14 miles are designated as BSS streams.

HERITAGE SITES : There are 74 Heritage occurrences. Seven community types, 25 plant species, ten animal species, and two rookeries are located in this RRA.

STATE AND FEDERAL LAND : Fort Massac State Park is the only state land in this RRA. Federally owned land consists of 12,000 acres in the Shawnee National Forest.